1. Field of Invention
This invention relates to a control device for use in a refrigeration circuit, and more particularly, to an improved device for controlling the volume of flow of refrigerant in a refrigeration circuit.
2. Description of The Prior Art
FIG. 1 shows a conventional refrigeration circuit for use, for example, in an automobile air conditioning system. The circuit includes compressor 1, condenser 2, control device 3, capillary 4, evaporator 5 and accumulator 6 serially connected. The output of accumulator 6 is also connected to the input of compressor 1.
With reference to FIG. 2, control device 3 includes tubular casing 31 through which refrigerant flows in the direction of the arrow. First wall 32 and second wall 33 are disposed on the interior surface of tubular casing 31 and are fixed a predetermined distance apart. First wall 32 and second wall 33 enclose interior chamber 36 of control device 3. First wall 32 has a plurality of holes 321 and second wall 33 has longitudinal bore 331. Longitudinal bores 331 widens into valve seat 332 on the interior side of second wall 33, that is, the side facing interior chamber 36.
Bellows 34 is disposed in interior region 36 and is fixed at one end to first wall 32. Valve element 35 is fixed at one end to the other end of bellows 34 and extends into spherical sealing element 37 at its other end. Spherical sealing element 37 engages valve seat 332 to control the flow of refrigerant fluid through longitudinal bore 331.
Bellows 34 contains a fluid which is either the same refrigerant used in the refrigeration circuit or is a fluid which has a greater saturation pressure than the refrigerant used in the refrigeration circuit. The fluid within bellows 34 is maintained in a saturated state and, therefore, the pressure of the fluid depends upon the temperature of the refrigerant in tubular casing 31. Bellows 34 will expand due to the pressure of the fluid within and due to its recoil strength. When bellows 34 expands, valve element 35 moves to the right in FIG. 2. However, bellows 34 will contract due to the pressure of the refrigerant within tubular casing 31. When bellows 34 contracts, valve element 35 moves to the left in FIG. 2. Control device 3 operates to maintain a balance between these opposing pressures and therefore, the operation of control device 3 is dependent on the degree of subcooling of the refrigerant at the outlet side of condenser 2.
In operation, if compressor 1 is not driven, the refrigerant fluid stagnates in the refrigeration circuit. In this situation, the pressure of the refrigerant at the outlet side of condenser 2 will always be less than the combination of the pressure of the fluid within bellows 34 and its recoil strength. Bellows 34 expands moving valve element 35 to the right in FIG. 2. The spherical sealing element of valve element 35 closes valve seat 332 of longitudinal bore 331. Valve seat 332 will remain closed until compressor 1 is driven and fluid circulates in the conduit between condenser 2 and control device 3.
When the conduit between condenser 2 and control device 3 is filled with refrigerant and the pressure of the refrigerant at the outlet of condenser 2 is greater than the combination of the pressure of the fluid within bellows 34 and the recoil strength of bellows 34, bellows 34 contracts moving valve element 35 to the left. Valve seat 332 is opened in accordance with the degree of movement of valve element 35. The degree of opening of valve seat 332 is therefore dependent on the degree of subcooling of the refrigerant. The size of the opening at valve seat 332 increases as the degree of subcooling of the refrigerant increases. Therefore, the degree of subcooling of the refrigerant fluid is maintained constant by the operation of the bellows 34. The desired degree of subcooling for the refrigerant can be predetermined by selection of the refrigerant and the recoil strength of bellows 34.
If the level of refrigerant in the refrigeration circuit becomes insufficient, the refrigerant will assume both the liquid state and the gas state. Gas and liquid will be mixed and the temperature of the mixture will become a saturation temperature, that is, since both forms are present in the circuit the refrigerant is saturated at that temperature. The pressure within bellows 34 will increase due to its dependence upon the temperature of the refrigerant within tubular casing 31. Since the refrigerant within bellows 34 is always saturated, and since it has a saturation pressure at least equal to the saturation pressure of the refrigerant fluid in the circuit, bellows 34 will expand to the right. Operating valve 35 will close valve seat 332 of longitudinal bore 331. The volume of the refrigerant which circulates is immediately reduced and the pressure of the refrigerant at the outlet side of compressor 1 will be abnormally decreased. As a result, the degree of superheating of the refrigerant at the inlet side of compressor 1 will be rapidly increased, and the functioning of compressor 1 may be abruptly stopped.